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Lecture 9.pptx

Lecture 9.pptx - Lecture 9 FLOW DEVICES PITOT TUBE H...

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FLOW DEVICES: PITOT TUBE Open channel flow H. Pitot (1695-1771) Impact tube or stagnation tube Bent and transparent (2) (1) (2) (h 2 ) (h 1 ) (P/  + gz + V 2 /2) = dW n,f /dm – F V 2 = negligible because fluid is stopped, dW n,f /dm = 0, z 1 = z 2 (P 2 – P 1 )/ – V 1 2 /2 = – F (1) Inside Pitot tube, fluid is not moving P 2 – P atm = - g(z 2 – z) P 2 = P atm + g(h 2 + h 1 ) (2) P 1 = P atm + gh 2 (3) From (2), (3) and (1) V 1 = (2 gh 1 + 2 F ) 1/2 P atm Lecture 9 V 1 = (2 gh 1 ) 1/2
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VENTURI METER Named after G. Venturi (1746-1822). Apply B.E. between points (1) and (2). (P/  + gz + V 2 /2) = dW n,f /dm – F dW n,f /dm = 0, z 1 = z 2 (P 2 – P 1 )/ + (V 2 2 - V 1 2 ) /2 = – F (1) F is very small and can be neglected. Mass balance with constant density, V 1 A 1 = V 2 A 2 V 1 = V 2 A 2 /A 1 V 2 = (2(P 1 -P 2 )/ )/(1-A 2 2 /A 1 2 )) 1/2
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INCLINED VENTURI METER WITH A MANOMETER Apply B.E. between points (1) and (2). (P/  + gz + V 2 /2) = dW n,f /dm – F dW n,f /dm = 0, F = 0 From mass balance equation with constant density V 1 A 1 = V 2 A 2 V 2 (1- A 2 2 /A 1 2 ) = [2(P 1 -P 2 )/ + 2g (z 1 -z 2 )] 1/2 (1)
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